1. Field of the Invention
The present invention generally relates to copy-protected video playback systems and more particularly to protection against unauthorized copying of video signals from computing devices.
2. Description of the Related Art
The Digital Video Disk (DVD) format gives consumers the ability to view exceptional quality video. In many instances, DVD players have replaced VHS players for home movie viewing. In addition, the DVD player functionality is now a feature of many of the personal computers (PCs) that are sold on the consumer market. This is a valuable feature that allows consumers to watch DVD movies on the PC.
Concurrently, video converters have also become available to allow consumers to use the standard TV as a monitor for PC. A combination of the PC DVD player along with video converter allows consumers to play video games and watch DVD movies using a large screen display. However, the DVD format also allows individuals to make near commercial-quality VHS recordings from any unprotected DVD program. The consumer is able to connect the output signal of the converter to the input of a VCR where the DVD signal may be recorded. Since the movie is stored digitally on a DVD disk, a high quality copy can be made of the movie.
As DVDs increase in resolution, movie studios have become increasingly concerned about consumers' ability to make high quality copy of movies. If widespread copying of DVD movies resulted, movie studios would be forced to stop releasing movies on DVD or delay the release of quality movies on DVD.
A number of techniques have been developed to address DVD copy protection. A watermarking process has been contemplated which permanently marks each digital video frame with background noise. Watermark signatures can be recognized by video playback and recording equipment to prevent copying. However placing a watermark signature directly on the video frame presents obvious video quality clarity issues. In addition, a watermarking process contemplates new players or other equipment to support watermarking. These issues, along with the difficult task of obtaining a common compatible standard agreeable among the principal commercial entities, pose significant hurdles to a watermarking solution.
Other non-destructive solutions, from the video signal standpoint, have been proposed. Digital Copy Protection Systems (DCPS) have been developed whereby the DVD player and a digital TV or a digital VCR exchange keys and identification certificates to establish secure channels. In addition, Content Scrambling Systems (CSS) have been proposed as a form of data encryption to discourage reading media files directly from the desk. Here again, encryption keys are exchanged so the video is decrypted before being displayed by the display device. Like the proposed watermarking solution, both of these other proposals require significant additional hardware (and cost) for movie copy protection. In addition, the CSS proposal contemplates a preliminary licensing requirement before any hardware may be implemented.
One approach to copy protection of video signals by Macrovision Corporation of Cupertino, Calif. involves inserting pseudo-synchronization pulses during the vertical blanking interval of video signals and varying the output levels. This confuses the fast phase locked loops (PLLs) and auto-gain controls (AGCs) used on recording devices but does not significantly affect the slower PLLs and AGCs used on televisions.